Im a new guy. With a Thunderbolt...

I currently have a thunderbolt and a friend has been trying to talk me into rooting. I plan on doing it but not until I have some clarity. I want to know how to install a ROM and what a good one is. I want to know how to 'flash' things and if I should be doing it. I am new to this whole game as I have never rooted before so I am starting from scratch here. Any knowledge will help. Thanks!!